1. Field of the Invention
The invention relates to a device for spreading a carbon fiber hank into a carbon fiber band with a heating device and a spreading device arranged after the heating device in the traveling direction of the carbon fiber hank. Furthermore, the invention relates to a method for spreading a carbon fiber hank into a carbon fiber band, in which the carbon fiber hank is heated and then spread.
2. Discussion of Background Information
Carbon fibers are often used for producing fiber-reinforced plastic materials. Carbon fibers have a relative low mass with a relatively high tensile strength in their longitudinal direction. Carbon fibers are often embedded in a plastic matrix. If there are several layers of carbon fibers running in different directions in a matrix of this type, the increased tensile strength and thus the improved load can also be present in several directions.
Carbon fibers are generally supplied by the manufacturer in the form of carbon fiber hanks. These carbon fiber hanks are often wound on bobbins. Sometimes they are also placed in containers. The carbon fiber hanks are generally much too thick for the production of a composite material. For the production of a carbon fiber-reinforced composite material, it is generally desirable to have the individual carbon fibers lying mainly next to one another and in a few layers one on top of the other. The process is therefore that first a carbon fiber hank is spread and the carbon fiber band thus produced is fed with a weft insertion or laying device to a machine, e.g., a warp knitting machine with weft insertion or a multiaxial machine, which forms a fabric from respectively a plurality of carbon fiber bands arranged next to one another. Several groups of carbon fiber bands are thereby generally arranged in different orientations one on top of the other, e.g., in the form of a 0° layer, a 90° layer, a +45° layer and a −45° layer. The spreading and the laying of the carbon fiber bands are known per se.
It is also known that the spreading of a carbon fiber hank into a carbon fiber band is much more successful if the carbon fiber hank is heated before the spreading. In the case of carbon fibers that have already been provided with a sizing or a bonding agent, heating the carbon fibers likewise leads to the sizing or the bonding agent being heated, so that the lateral adhesion of the individual carbon fibers is weakened and the carbon fibers can be expanded more easily under a pressure acting on the carbon fiber hank.
There are several ways of heating. One known possibility is to act on the carbon fiber hank with heated air. However, if the flow conditions are unfavorable hereby, heating with heated air can lead to the carbon fibers becoming entangled in the carbon fiber hank, which in turn impairs the spreading or expanding effect.
Another possibility is to guide the carbon fiber hank over heated rollers. The heat is then transferred from the heated rollers to the carbon fiber hank. Although this embodiment has proven useful in principle, it requires a relatively high use of energy, because not only the carbon fiber hank but also the entire heated rollers have to be heated. Most of the heat is emitted unused from the heated rollers into the surroundings. Moreover, it is relatively difficult to react quickly to changes because of the thermal inertia of the heated rollers, e.g., to changes in the speed of the carbon fiber hanks. This can entail the carbon fiber hanks being overheated or not heated enough.